This invention relates to a rolling roll into which a sleeve of a high wear-resistance is incorporated to provide a working surface and, more particularly, a ceramic sleeve incorporated rolling roll wherein a ceramic sleeve is fitted on an arbor or a metal rolling roll body and improved so as not to cause displacement between the ceramic sleeve and the metal rolling roll body even if the rolling roll is raised in temperature during rolling, and a rolling mill into which the above-mentioned rolling roll is employed.
Recently, many attempts have been made to improve wear resistance of a rolling roll, as a result, many kinds of roll construction materials, that is, bearing steel, die steel, high speed steel and a special material such as tungsten carbide are used. Further, ceramics also has been used as material for rolling rolls. The ceramics is hard and has a sufficient wear resistance and a strong resistance against compression stress, however the ceramics is lacking in strength against tensile stress. Further, cemented carbide and ceramics cost higher than metal, therefore, it is desirable that they are used only in a portion of the rolling roll is in direct contact with material to be rolled during rolling and required to have wear resistance. Further, it is difficult to produce a large scale rolling roll of ceramics, so that sleeve-assembled rolling rolls have been used in order to solve the above-mentioned defect.
However, as mentioned above, since the ceramics is not strong against tensile stress, a conventional assembling method such as shrinkage fit, press fit, etc. can not be employed. In case the conventional assembling method is employed in assemblage of a ceramic sleeve and a rolling roll body, since the thermal expansion coefficient of ceramics is much smaller than a metal roll body, tensile stress is produced in the ceramic sleeve when the rolling roll temperature is raised during rolling, which results in early breakage of the ceramic sleeve.
Therefore, an assembling method wherein compression is previously added to a cemented carbide or ceramic sleeve has been developed.
There are various examples of such assembling methods, one of which is a method wherein a pressure chamber is provided between an end portion of a sleeve and a supporting member for fixing the sleeve, and the sleeve is fixed by pressure in the pressure chamber, which assembling method is disclosed in Japanese Patent Laid-Open Nos. 57-165107 (1982) and 59-1009 (1984). Another is a method wherein an average thermal expansion coefficient of a hard sleeve and a separate ring is made smaller than that of a rolling roll body, the sleeve and separate ring are assembled in the rolling roll body in a state that the rolling roll is extended more than the sleeve and the separate ring by raising the temperature thereof during assemblage, and compression stresses are applied on the sleeve sides when the assembled roll is cooled, whereby the sleeve is fixed, which is disclosed in Japanese Patent Laid-Open No. 59-35816 (1984). And still another is a method wherein a spacer which has a thinner effective thickness at time of thermal expansion than when shrank is used between a sleeve and a fixing device such as a nut, the spacer in a state of thermal expansion is assembled into a rolling roll body together with the sleeve, a disc spring, etc. and fixed by the nut, and then the spacer shrinks radially thereby to increase the deformation of the disc spring and give compression force on the side of the sleeve, which is disclosed in Japanese Patent Laid-Open No. 60-83708 (1985).
In the above-mentioned conventional techniques, a maximum constraining force for the sleeve is provided at a low temperature, the constraining force becomes weak as the temperature of the rolling roll rises, and the constraining force disappears when the temperature further increases, which results in free movement of the sleeve.